KEVOS® MAKEOS · Gears
Gear Hobbing Plan (Time, Hob Life and Cost per Gear)
How long does each gear take to hob, what share of hob sharpening and hob cost falls on each gear, and what does the batch cost?
Plan of a gear hobbing job: hob and work speeds, approach and total hob travel, cutting and floor-to-floor time per gear with stacked blanks (as the hobbing time tool), machine-time cost with set-up spread over the batch, sharpening cost per gear from the gears cut between sharpenings, hob cost per gear over the hob’s sharpening life, the cost per gear and for the batch, and the hob speed against the machine maximum.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Gear teeth | Number of teeth on the gear. | |
| Hob starts | Number of starts on the hob. | |
| Hob diameter | mm | Outside diameter of the hob. |
| Cutting speed | m/min | Cutting speed for the hob and material. |
| Axial feed per work revolution | mm/rev | Axial feed of the hob per revolution of the work. |
| Face width | mm | Face width of the gear. |
| Tooth depth | mm | Whole depth of the tooth. |
| Helix angle | ° | Helix angle of the gear. |
| Overrun | mm | Extra hob travel past the face. |
| Blanks per stack | Blanks cut together in one stack. | |
| Load and unload time per stack | min | Time to load and unload a stack. |
| Machine and tooling | ||
| Largest hob spindle speed | rpm | Highest hob spindle speed of the machine. |
| Machine and labour rate | $/h | Machine plus operator rate. |
| Set-up time | min | Set-up time for the batch. |
| Gears in the batch | Gears in the batch. | |
| Gears cut between sharpenings | Gears the hob cuts before it needs sharpening (your value). | |
| Cost of one sharpening | $ | Cost of sharpening the hob once. |
| Sharpenings in the hob’s life | Number of sharpenings the hob can take before it is scrapped. | |
| Hob price | $ | Price of a new hob. |
Method and formulas
- Hob speed n = 1000 V_c ÷ (π D_h); work speed = n × starts ÷ z; approach = √[h (D_h − h)]; travel = b ÷ cos β + approach + overrun (as the hobbing time tool).
- Cutting time per gear = travel ÷ (f × work speed) ÷ stack; floor-to-floor adds the load time ÷ stack.
- Cost per gear = rate × (floor-to-floor + set-up ÷ batch) + sharpening ÷ gears per sharpening + hob price ÷ [gears per sharpening × (sharpenings + 1)].
- Example: each gear takes 6.9709 min floor to floor and costs about 11.582; the batch costs 5,790.9.
Limitations
- Single pass at constant feed; roughing and finishing passes need their own lines.
- Hob life must match the speeds, feeds and material.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Quote a hobbed gear
- Compare stacking blanks for a batch
- See what share of cost the hob takes
Who it is for
- Gear engineers
- Estimators
- Process planners
What you get
- Hob and work speeds, travel and times
- Machine, sharpening and hob cost per gear
- Batch cost
Interpreting the result
- Stacking blanks spreads the approach and loading over several gears; it pays most on narrow gears.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3347–3349. Topic reference; no source tables or recommended settings are reproduced.
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Open the Gear Hobbing Plan (Time, Hob Life and Cost per Gear) calculator
